A laser spectrometer based on difference-frequency generation in periodically poled LiNbO3 (PPLN) has been used to quantify atmospheric formaldehyde with a detection limit of 0.32 parts per billion in a given volume (ppbV) using specifically developed data-processing techniques. With state-of-the-art fiber-coupled diode-laser pump sources at 1083 nm and 1561 nm, difference-frequency radiation has been generated in the 3.53-micrometers (2832-cm-1) spectral region. Formaldehyde in ambient air in the 1- to 10-ppb V range has been detected continuously for nine and five days at two separate field sites in the Greater Houston area operated by the Texas Natural Resource Conservation Commission (TNRCC) and the Houston Regional Monitoring Corporation (HRM). The acquired spectroscopic data are compared with results obtained by a well-established wet-chemical o-(2,3,4,5,6-pentafluorobenzyl) hydroxylamine (PFBHA) technique.
Abstract.A one-week in situ intercomparison campaign was completed on the Rice University campus for measuring HCHO using three different techniques, including a novel op-
Introducing difference frequency generation (DFG) it is possible to create laser sources applicable to high resolution spectroscopy in the mid-infrared. It may become a convenient method for the detection of trace gases. Preferably for this purpose are the atmospheric windows. Whereas with DFG in AgGaS2 the atmospheric window around 4.7 µm could be covered AgGaSe2 allows to produce radiation in the 8 - 13 µm window. In the latter region nearly all atmospheric trace molecules have characteristic bands. Therefore, we developed a spectrometer with the nonlinear material AgGaSe2.
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